A Workable Photon Drive?

byPaul GilsteronFebruary 22, 2007

A device called a Photonic Laser Thruster is making news since a December demonstration of the technology by its inventor, Young Bae. The founder of the Bae Institute in Tustin CA, Bae has pursued antimatter and fusion research for twenty years at places like SRI International and Brookhaven National Laboratory. His current work on photon thrust is raising some eyebrows, as noted in this news release from the Institute, which quotes the Air Force Research Laboratory’s Franklin Mead:

“I attended Dr. Bae’s presentation about his PLT demonstration and measurement of photon thrust here at AFRL. It was pretty incredible stuff and to my knowledge, I don’t think anyone has done this before. It has generated a lot of interest around here.”

In one form or another, something called a ‘photon drive’ has been in the back of inventors’ minds since the days of the German researcher Eugen Sänger, who published a designed he called a ‘photon rocket’ that would use gamma rays produced by the annihilation of electrons and positrons for thrust. The problem with that one is that you can’t control the exhaust stream, since highly energetic gamma rays penetrate any materials that would be used to contain them. And in any case, Sänger’s concept is a variation on an antimatter engine, which is not what Dr. Bae is up to.

Photons themselves, having no mass or charge, present obvious problems to anyone trying to get thrust out of them. Fortunately, they do impart momentum, which is how solar sails work. What Bae’s system does is to bounce photons using “…a photonic laser and a sophisticated photon beam amplification system.” Bouncing photons between spacecraft thousands of times is said to do the trick, producing measurable thrust that can be used in space applications.

In fact, according to the Institute’s Web site, “A small scale PLP, Photonic Laser Thruster (PLT) has recently been successfully demonstrated by Bae Institute, and the result has demonstrated the principle of PLP [Photonic Laser Propulsion] by amplifying photon thrust by 3,000 times.”

Keeping multiple spacecraft in precise formation (down to nanometer lengths) may be one outgrowth of this technology, and if so, it’s an important one. NASA’s MAXIM (Micro-Arcsecond X-ray Imaging Mission), for example, would use numerous spacecraft flying in tight formation in order to study black holes. The need for precise adjustment between independent craft has resulted in Bae’s Phase II study for NASA’s Institute for Advanced Concepts. Think space-borne interferometry, with the spacecraft kept in configuration through PLT and space tethers. The resultant formation, says the Bae Institute, will prove 100,000 times more precise than existing methods of flying spacecraft in formation.

Here’s a snippet from the Phase I study that preceded Dr. Bae’s current work for NIAC:

In addition to redefining and simplifying the existing NASA mission concepts, such as SPECS and MAXIM, PTFF [Photon Tether Formation Flight] enables other emerging revolutionary mission concepts, such as New World Imager Freeway Mission proposed by Prof. Cash, which searches for advanced civilization and in exo-planets Fourier Transform X-Ray Spectrometer proposed by Dr. Schnopper. As the present concept is more publicized, many other exciting concepts are expected to be inspired by PTFF. One of such possible NASA missions is the construction of ultralarge space telescope with diameters up to several km for observing and monitoring space and earth-bound activities.

If it will get New Worlds Imager working, I’m all for it. But will it? Here’s a link to David Livingston’s interview with Bae, in which he discusses PTFF as well as antimatter and fusion concepts. This New Scientiststory on Bae’s work is also helpful. Less helpful, perhaps, is the claim on the Bae Institute’s Web site, describing photonic laser propulsion as “Our patent-pending, innovative, yet highly realistic, photon propulsion concept capable of accelerating spacecraft to near light speed without propellant.”

Perhaps, but first things first. Let’s get those space interferometry missions working, and on that score, NIAC’s Robert Cassanova reminds us in New Scientist that alternative concepts are still in play.

It’s not really a “breakthrough” IMHO, more of a refinement. Multiple reflections of a laser would no doubt improve the efficiency of the thrust, but eventually the loses will add up and there’s only so many reflections that can be achieved for anything vaguely like a probe launcher, for example. Still as a station-keeping system for formation flyers this is pretty cool.

Sänger was technically a Czech, born in Bohemia, though he did his engineering studies in Austria, and you’re right, I do see him referred to as an Austrian, though he seems to have done most of his work in Germany.

One should note that as the vehicle being accelerated approaches the speed of light, the number of reflections that can be done declines. The reason is that the light is red shifted (twice) when it’s reflected off the vehicle, and so loses energy. For a vehicle traveling close to the speed of light, almost all the energy of the light is transfered to the vehicle at the first reflection.

If you have to worry about red-shift, the photonic engine will have you moving quite fast. A good problem to have. An interesting question is how well would the mirror materials stand up to stronger lasers. It sounds like they are working with 10 watt lasers.

If one used the vapor core nuclear reactor to power a laser.
The vapor core nuclear reactor (VCR) with magneto-hydrodynamic (MHD) conversion to electricity — thus VCR-MHD — and that the vapor used is a mix of uranium tetrafluoride (UF4) and potassium fluoride (KF), to optimise ionisation in the MHD channel. The VCR-MHD operates at over 2000K (2600K inlet, 1550K outlet). Specific mass, depending on design details, is between 0.4 to 0.6 kg/kWe. This would be about 40-60 tons for 100MWe.

The 20,000 to 100,000 mirror amplification boost would reduce the power and laser requirements for equivalent acceleration.

Issues of targeting. Plus I would think that it would work best with better vacuum. At least outside of the atmosphere for the acceleration to a fraction of light speed.
Ground launch has reduced requirements and by definition would have to work through the atmosphere.

Brian, anything that leaves most of the heavy stuff on the ground, as Jordin Kare talks about in the presentation you link to, is all to the good, which is why variations on these laser concepts seem so attractive to me. Thanks for your good work on the lasers and ISP — much appreciated. For those who don’t know it, the Landis paper that Brian links to is a fine backgrounder based on Geoff’s NIAC work before he went to NASA.

When I look at the atlas and when I visited Austria it was definately NOT part of Germany. Berfore WWI it was the Austro-Hungarian Empire, parts of which are now in modern day Germany, but if he was Czech, that would have been after WWI and I dont think that any of Czecoslovakia is in Austria or Germany it simply split into the Czech Republic and Slovakia in the 80’s. Interstingly, the Austrians do not speak German either, it is similar but they do speak Austrian which is a different dialect.

I designed a laser photon thruster of my own 33 years ago in 1974.
It was intended for interplanetary propulsion . tHE GOAL OF THE LASER
PHOTON THRUSTER WAS TO COUNTER BALANCE THE PULL OF THE SUNS
GRAVITY IN INTERPLANETARY SPACE THUS ALLOWING THE SPACE CRAFT
TO MAINTAIN A CONSTANT OUTBOUND VELOCITY OF 30 KM/SEC WITH OUT
SLOWING DOWN UPON DEPARTING THE EARTH AT 1 AU FROM THE SUN .
I ALSO USED IT IN A DESIGN FOR AN INTERSTELLAR PERCURSER MISSION IN THE YEAR 1979. THE LASER PHOTON ENGINE WAS USED TO KEEP THE VEHICLE FROM SLOWING DOWN FROM THE PULL OF THE SUNS GRAVITY
AFTER IT CARRIED OUT A GRAVITATIONAL ASSIST BY FLYING BEHIND THE SUN AND THEN BEING FLUNG OUTWARD BY THE SUNS GRAVITY INTO INTERSTELLAR SPACE . IT COULD OBTAIN 100-150 KM SECOND FROM SLINGSHOTTING AROUND BEHIND THE SUN, AND THEN USING THE LASER
PHOTONIC THRUST TO KEEP THE VEHICLE FROM SLOWING DOWN AS
IT MOVED OUTWARD FROM THE SUN ,AFTER SLING SHOTTING AROUND IT .
BOTH LIGHT, AND GRAVITY DECLINE PROPORTIONAL TO THE INVERSE
SQAURE OF THE CHANGE IN DISTANCE . THE LASER THRUST THUS WOULD COUNTERBALANCE THE PULL OF THE SUNS GRAVITY AS YOU MOVE AWAY FROM THE SUN IN DEEP SPACE .ONLY A TINY BIT OF PHOTONIC THRUST
IS REQUIRED TO DO THIS . MY ENGINE DESIGN USED A BUNDLE OF ELECTRICALLY PUMPED CARBON DIOXIDE LASER TUBES TO GENERATE
MULTIPLE LASER BEAMS WHICH WERE THEN REFLECTED OFF A CONVEX OR PARABOLIC MIRROR INTO SPACE THROUGH A CYLINDRICAL NOZZLE TUBE.
THE DELIVERED A SPECIFIC IMPULSE OF 30,000,000 SECONDS: BUT
150,000,000 MEGAWATTS OF LASER LIGHT BOUNCED OFF A 100 % PERFECT
MIRROR IS REQUIRED TO PRODUCE JUST 1 NEWTON OF LASER PHOTONIC THRUST . TIMOTHY MAYES

Pardon my ignorance, but since the power of this concept seems to be based on rapid reflection between precisely spaced surfaces or spacecraft where does the thrust power go? Is it simply the push against the other surface or spacecraft or can the laser be beamed out into the vacuum of space after it has been sufficiently energized by the repeated reflections off of whatever surface is used? Dumb question but the articles I have read don’t address this issue at all.

Photons can only impart momentum if they are deflected. A laser itself is not a self-propelling device, as it is not shedding mass. A laser pointed at a mirror will impart momentum to the mirror, which for any reasonably sized laser and mirror will not move it at all, especially outside hard vacuum and freefall.

The reason this technology has never been used in the many decades it has been known and proven is because unless you are using the sun itself as your source of photons, you’re throwing a grape at a Panzer.

First, photons impart momentum whether they’re deflected or absorbed and then their energy is re-radiated. “Deflection”/reflection produces double the thrust.

Lasers do propel themselves because photons have momentum, but the thrust produced is miniscule. 1 newton for 1 second requires beaming 300 MJ or energy, thus there are no lasers that currently produce much thrust at all. The mass-loss is the ‘energy mass’ of the energy produced as photons.

Your last point is true, but multiple reflections enhance the thrust perhaps many thousand-fold.

One of the key issues that any form of experimental rive system has is that in principal it may work well on paper or in the laboratory, however you must look at some of the key principal issues surrounding such things.

Even if you can get a workable drive, any craft that would use something such as this system, that has the potential to drive a space vehicle faster than we have ever gone before. You must look at was to protect it and make it capable of travelling in alternative directions fast enough to prevent pre-partial and post partial wake damage. As if you travel fast enough in space you could over time see a visible sand blasting type of degradation of the vehicle. As space may be relatively empty but it still contains around 5 particles per “1 Meter squared”. This of course is nothing compared with the damage that small objects can cause! It may however be possible to create a primitive style of force field if you could some how surround the craft in a cloak of plasma or a rotating magnetic field, maybe a combination of them both so that you nudge that particles away or around the craft. Thus ensuring that in any case, any vehicle travelling in space at any real speed, i.e. the one hundred thousand to a million miles per hour plus range preferably higher to allow for true interplanetary transportation, will be able to cope. As just like travelling in an atmosphere unless you find some way to improve the aerodynamics or in this case “spaceialdynamics” any craft/vehicle will have an inherent speed limit regardless of the engine / drive type used.

@johnniea, April 9th, 2007 at 16:27,
@malte, February 23rd, 2007 at 8:37 @

Err.. Eugen Sänger was not a Czech. Both Eugen and Sänger are German names. Sänger ist German for singer (like in “to sing”). Two World Wars changed alot of things in europe. At the time Sänger was born, like centuries before, there was a large german population in Bohemia. Bohemia was under German-Austrian rule for several centuries, nearly a thousand years.
At the same time, Austria was part of Germany, like Bavaria, Saxony or Hessia (Hesse) are parts of Germany. Vienna was even the capitol of Germany at that time. It was after the Prussian-Austrian war, which Austria lost, that Austria got (forcefully) seperated and thrown out.

Austrian is not a different language from German. Its a German dialect, just like Bavarian, Saxon etc. Its spoken version is more related to Bavarian or other South-German dialects than British-English is related to American-English. And you would not call BE and AE different languages, would you? In its written form there is no difference at all, while there is a difference between BE and AE, like in “color” (AE) and “colour” (BE), or using different words like “vacation” and “holiday”. You would not find these kind of differences between Ausrian-German and e.g. Swabian-German or Bavarian-German.

hi guys,
can we get down to cases here?
can this idea really get, say, a 20 ton space craft off the ground? or if it was already in orbit, could it propel it to alpha centauri, in less than 7 years, with a human crew?
just asking.

Need to think about power to weight ratio. People mention the space shuttle and the large power requirements ignoring the first step which will be very lightweight probes. Last time I looked at this the magnitudes were down to several kilowatts/m/m to achieve acceleration of g. Also energy put into angular instead of linear momentum of the photon is a complete waste of power.

In Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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